Are there any modulating gas condensing boilers where the modulation can be both automatic and also manual?
I believe there are gas condensing boilers where the gas burning rate can be modulated, and the amount of modulation is set by the return water temperature.
Can someone please tell me if I should be able to find any boilers where, in addition to the above, the amount of modulation can also be set by hand? That is, the maximum gas rate can be easily set to a reduced level just by turning a knob, without needing anything like a manometer and screwdriver?